1. Field of the Invention
The invention relates to a power transmission apparatus, a power outputting method and a hybrid vehicle, and more particularly to a power transmission apparatus and a power outputting method which can output at least a part of power output by a prime mover to a drive shaft in a mechanical form, and a hybrid vehicle equipped with a prime mover which can output at least a part of power to a drive shaft in a mechanical form and a power adjusting apparatus which can transmit the power between the drive shaft.
2. Description of the Related Art
As an apparatus for converting an output torque of a prime mover such as an internal combustion engine so as to transmit power, in recent years, there is suggested a structure obtained by combining an electric motor with a power distribution performed by a planetary gear mechanism, and a structure for distributing power by employing a pair-rotor electric motor having two relatively rotatable rotors so as to utilize a slip between the rotors, in place of a torque converter using fluid. As a structure which employs the power transmission apparatus for transmitting the power to a plurality of drive shafts, for example, there is known a structure shown in Japanese Patent Laid-Open Publication No. HEI9-175203. The power transmission apparatus mentioned above is excellent in view that an advantage of a high efficiency can be obtained since the power is not transmitted to fluid or the like.
However, in such a power transmission apparatus, there has been a problem that there were some cases where a sufficient torque can not be obtained when reversely rotating the drive shaft. This is due to the following reasons. In the case of the power transmission apparatus which can output at least a part of the power output by the prime mover to the drive shaft in a mechanical form, it is generally impossible to reversely rotate the prime mover such as an engine, even in the case of reversely rotating the drive shaft. Accordingly, there is performed a control of reversely rotating the drive shaft while normally rotating the engine. In the case where the power transmission apparatus is provided with a battery and is sufficient to use an electric power stored in the battery, it is sufficient to stop the engine and reversely rotate the drive shaft only by a torque of the electric motor. However, in the case where it is impossible to respond to the situation only by the electric power stored in the battery and the case where a state of charge of the battery is low, it is necessary to generate a reverse rotation torque in the electric motor while generating electric power using the power of the engine so as to reversely rotate the drive shaft. In such cases, the torque output to the drive shaft becomes a torque obtained by subtracting an output torque in a normal rotating direction generated by the engine from a torque in a reverse rotating direction generated by the electric motor connected to the drive shaft.
The problem mentioned above can not be overlooked in a so-called hybrid vehicle in which the power transmission apparatus in accordance with the above aspect is mounted, since a high torque can not be obtained particularly at a time when the vehicle moves backward. In the power transmission apparatus outputting at least a part of the power output by the prime mover to the drive shaft in accordance with a mechanical form, the same problem occurs both in an electricity distribution type in which power is distributed using an electric motor having a pair of relatively rotating rotors or in a mechanical distribution type employing a three-shaft type power distributor such as a planetary gear or the like. Here, if a planetary gear is employed for distributing the power in the latter case, since the number of revolutions and the torque of each of the shafts have a simple proportional relation determined by the number of teeth, there is a problem that when the drive shaft is reversely rotated and the number of revolutions and the torque of the prime mover are high, the number of revolutions and the toque of another shaft are out of allowable ranges. Accordingly, the number of revolutions of the drive shaft was limited in this respect as well.
An object of the invention is to provide a power transmission apparatus, a power outputting method and a hybrid vehicle equipped with the power transmission apparatus which can solve the problems mentioned above and increase freedom in controlling a number of revolutions of a drive shaft and a torque in the case of reversely rotating the drive shaft.
In order to solve at least a part of the object mentioned above, in accordance with the invention, there is provided a power transmission apparatus which can output at least a part of power output by a prime mover to a drive shaft in a mechanical form, comprising:
a prime mover adjuster adjusting a state of the power output from the prime mover;
a power generator connected to the prime mover in such a manner as to be capable of electrically regenerating at least a part of the power output from the prime mover;
an electric motor connected between an output shaft of the prime mover and the drive shaft and capable of normally rotating so as to rotate the drive shaft in the same direction as a rotation direction of the output shaft and reversely rotating so as to rotate the drive shaft in a reverse direction to the rotation direction of the output shaft; and
a controller rotatively driving the electric motor in the reverse direction to that of the output shaft of the prime mover by using an energy regenerated by the power generator and controlling the prime mover adjuster so as to control a state of the power output from the prime mover to an amount lower than that in the case of normally rotating the drive shaft, at a time of reversely rotating the drive shaft.
Further, in accordance with the invention, in correspondence to the power transmission apparatus mentioned above, there is provided a power outputting method which outputs at least a part of power output by a prime mover to a drive shaft in a mechanical form, comprising the steps of:
adjusting a state of the power output from the prime mover;
electrically regenerating at least a part of the power output from the prime mover by a power generator connected to an output shaft of the prime mover, and normally rotating the drive shaft in the same direction as a rotation direction of the output shaft by an electric motor connected between the output shaft of the prime mover and the drive shaft or reversely rotating the drive shaft in a reverse direction to the rotation direction of the output shaft; and
at a time of rotating the drive shaft in a reverse direction, rotating the electric motor in the reverse direction to that of the output shaft of the prime mover by using an energy regenerated by the power generator and controlling a state of the power output from the prime mover to an amount lower than that in the case of normally rotating the drive shaft.
In accordance with the power transmission apparatus and the power outputting method mentioned above, at a time of rotating the drive shaft in the reverse direction, the electric motor is rotated in the reverse direction to that of the output shaft of the prime mover by using the energy regenerated by the power generator, and the state of the power output from the prime mover is controlled to an amount lower than that in the case of rotating the drive shaft in the normal direction. Accordingly, it is possible to increase the power in the reverse direction output from the drive shaft.
Further, in the power transmission apparatus or the like mentioned above, the structure may be made such that the power generator is a pair-rotor electric motor equipped with two relatively rotatable rotors, wherein one of the pair of rotors is connected to the output shaft of the prime mover and another of a pair of rotors is connected to the drive shaft. In the case where the pair-rotor electric motor is employed for the power generator, in power distribution, power is taken out as an electrical energy in accordance with a slip number of revolutions corresponding to a relative number of revolutions of a pair of rotors, and the remaining energy is output to the drive shaft in a mechanical form, so that the apparatus can be made compact.
In this case, when the electric motor mentioned above can be selectively connected to one of the output shaft of the prime mover and the drive shaft and the drive shaft is reversely rotated, the electric motor may be connected to the drive shaft. In this case, it is possible to connect the electric motor to the output shaft of the prime mover so as to realize a so-called overdrive state and it is possible to connect the electric motor to the drive shaft so as to realize a so-called under-drive state. Since there is provided the structure for switching the shaft for connecting the electric motor, no recirculation of the energy is generated in either cases. In the case of reversely rotating the drive shaft, since the drive shaft can not be reversely rotated at a number of revolutions above the number of revolutions (including the rotation direction) of the prime mover, the structure may be made such that the electric motor is connected to the drive shaft, in this case.
Further, as the prime mover mentioned above, it is possible to employ an internal combustion engine which performs an explosive combustion by mixing an air sucked via an intake valve with a fuel. As the fuel, it is possible to use various kinds of fuels such as gasoline, light oil, alcohol, propane gas, and natural gas. Of course, it is possible to utilize other prime movers such as a gas turbine. In the case of using the internal combustion engine as the prime mover, the structure may be made such that means for controlling an amount of intake air and an opening and closing timing of the intake valve is provided as means for adjusting a state of power of the prime mover.
The structure may be made such that the power transmission apparatus is provided with a battery storing an electric power regenerated by the power generator so as to drive the electric motor using at least a part of the electric power stored in the battery in addition to the regenerated electric power at a time when the controller reversely rotates the drive shaft. Since the electric power in the battery is used in addition to the regenerated electric power, it is possible to output a high power to the drive shaft within an allowable range of a residual capacity of the battery.
As another structure for distributing the power from the prime mover, there is a so-called mechanical distribution aspect. This structure is provided with three shafts, and employs a three-shaft type power transmission mechanism in which the power input to and output from the one shaft is determined by the power input to and output from other two shafts, wherein one of three shafts in this mechanism is connected to the output shaft of the prime mover, another one shaft is connected to the drive shaft, and the remaining one shaft is connected to the power generator. Further, the electric motor is connected to the drive shaft. By making the structure in the above manner, it is possible to output at least a part of the power output from the prime mover to the drive shaft in a mechanical form. When employing the structure of the mechanical distribution type, it is not necessary to employ the pair-rotor electric motor and it is possible to simplify the structure.
In accordance with the invention, there is provided a hybrid vehicle equipped with a prime mover which can output at least a part of power to a drive shaft in a mechanical form and a power adjusting apparatus which can transmit the power between the drive shaft, comprising:
a prime mover adjuster adjusting a state of the power output from the prime mover,
wherein the power adjusting apparatus comprises:
a power generator capable of electrically regenerating at least a part of the power output from the prime mover;
an electric motor connected between an output shaft of the prime mover and the drive shaft and capable of normally rotating so as to rotate the drive shaft in the same direction as a rotation direction of the output shaft and reversely rotating so as to rotate the drive shaft in a reverse direction to the rotation direction of the output shaft; and
a controller rotatively driving the electric motor in the reverse direction to that of the output shaft of the prime mover by using an energy regenerated by the power generator and controlling the prime mover adjuster so as to control a state of the power output from the prime mover to an amount lower than that in the case of normally rotating the drive shaft, at a time when the vehicle moves backward.
In this hybrid vehicle, when the vehicle moves backward, the prime mover adjuster is controlled so as to control the state of the power output from the prime mover to be lower than that in the case of normally rotating the drive shaft. Accordingly, in the case of reversely rotating the drive shaft, the drive torque of the drive shaft which is taken out as the difference between the torque of the electric motor and the torque of the prime mover can be made large as compared to the state in which the prime mover is not controlled. As a result, it is possible to make the state of the power at a time of backward movement close to the desired power.
The invention can be applied to a four wheel drive hybrid vehicle. Further, in addition to vehicles, the invention can be employed for ships, machining tools or other equipment.